Method of treating kyanite concentrates



. use as grog.

United States Patent 6 METHOD OF TREATING KYANITE CONCENTRATES' Voldemars D. Svikis, Ottawa, Ontario, (Ianadanassignor to Her Majesty the Queen in the right of Canada, as

represented. by the Minister of.Mines and Technical.

Surveys.

No Drawing; Application April 16, 1956 Serial No. 578,202

6.. Claims. (Cl. 106- 65) This inventionrelates to a-method-tor producing-a volumestabledense and highlyrefractory material from.

kyanite concentrates.

Thisuapplication is a continuationin-part.of'; application, Serial No- 545,504, filedtNovember 7, 1955,. nowabandoned.-

Kyanite,.on being heated is convertedto mullite which is a.. valuable. highly refractory material.

but the kyanite obtainable. from knownworkable; de-

posits in North. America experiencesa rapid, relatively large. expansion during conversion to mullite and resultsin an' easily. shattered, porous, friable product.

For the. production'of superduty or-mullite type firebrick or shapes, which demand high. refractoriness, fairly;

porosity and afriable mechanically weak finished prod.---

uct, which. is alsounstable-volumetrically on beingreheated. Even though calcined at high temperatures and finely ground, similar results: areobtained when incorporated in firebrick. compositions. Further. in the production of alumina-silica firebrick and the like it is normally. requiredv that. the. no11-plastic:ingredient in composed-0f. a substantial percentage of coarse particles, so that optinnmi grading of. grain. sizes: can be realized. But to purify the kyanite ore, it must be ground to a relatively fine grainsize to insure that the kyanite particles are freed; from associated mineral. impurities.

Because of these difiiculties a particular type of kyanite obtained in India has been; in.hi gh demand for many years for the production of mullite type refractories. It also expands when heated to advanced temperatures, but the result is a hard, comparatively dense product, which can be readily crushed and graded for The reason for the difference in behaviour of the two types of kyanite has been attributed to: (1) India kyanite is massive, whereas North American kyanite normally'occurs as disseminated bladed crystals; (2) the former usually contains some corundum, the latter contains some excess silica.

According to accepted practice in industrial mineral industry in order to accomplish a sufiicient degree of beneficiation, the ore of the disseminated type of kyanite is ground to a relatively fine grain size and the associated minerals removed by means of magnetic separation, flotation, etc. This provides a kyanite concentrate, which contains in excess of 90 percent kyanite mineral in finely divided form.

It is the object of the present invention to provide a method of treating North American kyanite concen Kyanite occurs inconsiderable amounts in. Canada and theUnited-States.

trates to produce a dense, volume-stable and high1y re j-i. fr'actory aggregate (in .form .of briquettes -or bricks) -from-f which grog can be de 55.1? hq..mfi. ll f.a tl il ofi superduty and/or mullite. type firebrick-andthe1ike.---

It has been foundthat additives lsuch as phosph'oricli acid, phosphorus pentoxide and soluble, aluminumphos: phates, each act asamineraIiZer. causing. an,.in.timate intergrowth of mullite crystals whenfthe relatively pure, kyanite concentrate is heated with the phosphateaddi-l tive toform a dense and volume-stable mullitefproduct.

The k'yanite concentrates having a grain size, which, will passat least200mesh ,sieve and preferably fiher,is

uniformly mixed with 0:1 to .Spercnt ofthe phosphate additive; The additives are preferably mixed 01'. d

persed in the optimum amount of'tempering wate re-f 'quired prior to dry-pressing the batch into briquettes. 1

Thisinsures maximum ease of uniform distribution of" theadditive in ..the;-.ba tch. The additive is more. effective with; the; most finely ground kyanite concentrate and with kya it: oncentrate. which. is not. S'Q.fil1& butcontains more impurities, since the impuritiesthemselves act. as a fluxand tend.thus to.increase-density,--but at-;f i

the same time the impurities reduce the refractorine's's' of "the product. The particular proportion of "phosphate additive used;-. within, the. range specified is thus gov v ernedf by thedinensss;andrpurityof thekyanite concen-j trate. 1

The. preparedbatch isf-ormed into briquettes under: a;

pressure. of 2,'0002 to;"10;009' p. s3. i; anda'fired at a tem perature of at least 1550 C. to transform the kyanite into a volume-stable mullite. product... The. maximumtemperature employed is below the fusion temperature of mullite (abovea1800 C.). ImgenerahlGOOit C. is a are-maintained at the firing-temperaturewithin the spec ifiedrange, known; as soaking time, is ()to 10 liours No -practical advantage has-been found by. using: a- .soaking time oflsubstantially more zthanzlOshours. The most desirable: firing. temperature; within' the. specified range and time: of soaking: a particularrrnaterial' is readily 1 de termined by test as will'be apparent. The briquettes. may. beainxtheiformnof brick andiused assuch, butsince; theiproductzisz'most widelyiusedxinethe form; of; grog or aggregate the briquettes: are usually"- crushedand screenedrto provide aagradedsgrog;

To illustrate: the... tfect of; the; method the following'r comparative results are given.

(1) A kyanite. concentrate containing 94% kyanite I where D is the dry weight of the briquette, W is the water saturated weight and V the volume of the briquette.

(2) Batches of the same kyanite concentrate ground to pass a 200 mesh sieve without the organic binder,

mixed with varying amounts of the phosphoric acid as an additive were formed into briquettes under a pressure of 10,000 p. s. i. and fired at 1600. with the following results:

Percent Apparent Soaking Time, hours additive Porosity,

Percent 6 2 17. 3 13. B 4 6. s as" 7 0.' l i 8 0.

When the soaking time was 10 hours the apparent porosity was respectively 15.2, 10.2, 1.0, 0.5, 0.2, 0.2 and 0.2%. f i

(3) The same kyanite concentrate ground to-pass a 270' mesh sieve and without the organic binder, mixed with varying small amounts of the phosphoric acid as an additive were formed into briquettesunder a pressure $110,000 p. s. i. and fired at 1700" C. with the following resu ts:

Tercent Apparent additive Porosity,

Booking Time,houra Percent (4) The same kyanite concentrate ground to pass a 325;.mcsh sieve and without the organic binder, mixed with varying small amounts of the phosphoric acid as an additive were formed into briquettes under pressure The particular proportions of phosphate additive used within the range specified is thus governed not only by the fineness and purity of the kyanite concentrate but also by the firing temperature and the soaking time at this temperature.

In each case when the apparent porosity of the briquettes was under 1 percent the briquettes were hard,

dense and volume-stable owing to the transformation of the kyanite to mullite in the presence of the phosphate additive. When the briquettes were broken down, the

product fractured into discrete, hard, substantially volnine-stable fragments to form a grog, which can beea sily graded into desirable grain sizes.

What is claimed is:

I. A method of treating concentrates of disseminated type kyanite to produce a dense, volume-stable product which comprises finely dividing the concentrates to pass through a screen havinga'tleast 200 meshes per inch, uniformly mixing the concentrate with at least 0.1% by weight of an additive being one of a group consisting :of phosphoric acid, phosphorus pentoxide and so]- uble aluminum phosphates and tempering water, form ing the mixture into briquettes under a pressure of 2,000 to 10,000 p. s. i. and firing the briquettes at a tempera ture of not less than 1550 C. and less than the-fusion temperature of mullite to convert the kyanite into a dense, volume-stable mullite product.

2. The method as defined in claim 1 wherein the fired briquettes are crushed to produce dense, volume-stable and highly refractory grog.

3. A method of producing a dense, volume-stable refractory aggregate which comprises mixing a substan tially pure concentrate of disseminated type kyanite having a particle size less than minus 200 mesh with 0.1 to 8% by weight of an additive, being one of a group consisting of phosphoric acid, phosphorus pentoxide and soluble aluminum phosphates and tempering water, forming themixture into briquettes under a pressure of 2,000 to 10,000 p. s. i. and firing the briquettes without fusion at a temperature not less than 1550 C. to convert the kyanite into a dense, volume-stable mullite product.

4. The method as defined in claim 3 wherein the fired briquettes are crushed to produce dense, volume-stable and highly refractory grog.

5. The method defined in claim 4 wherein the additive is dissolved in water and the mixture to be briquetted is tempered with the solution so formed.

6. The method defined in claim 4 wherein the briquettes are substantially maintained at a temperature between 1550 and 1800" C. for a periodof time between zerohand 10 hours to ensure complete conversion of the kyanite to a dense, volume-stable mullite product.

References Cited'inthe 'file of this patent UNITED STATES PATENTS 

1. A METHOD OF TREATING CONCENTRATES OF DISSEMINATED TYPE KYANITE TO PRODUCE A DENSE, VOLUME-STABLE PRODUCT WHICH COMPRISES FINELY DIVIDING THE CONCENTRATES TO PASS THROUGH A SCREEN HAVING AT LEAST 200 MESHES PER INCH, UNIFORMLY MIXING THE CONCENTRATE WITH AT LEAST 0.1% BY WEIGHT OF AN ADDITIVE BEING ONE OF A GROUP CONSISTING OF PHOSPHORIC ACID, PHOSPHORUS PENTOXIDE AND SOLUBLE ALUMINUM PHOSPHATES AND TEMPERING WATER, FORMING THE MIXTURE INTO BRIQUETTES UNDER A PRESSURE OF 2,000 TO 10,000 P. S. I. AND FIRING THE BRIQUETTES AT A TEMPERATURE OF NOT LESS THAN 1550*C. AND LESS THAN THE FUSION TEMPERATURE OF MULLITE TO CONVERT THE KYANITE INTO A DENSE, VOLUME-STABLE MULTI PRODUCT. 